Tubular slug reducer

ABSTRACT

The flow line  10, 12, 30  is provided for reducing axial separation of different density fluids passing through the flow line, such as gas and liquids. The flow line is provided with one or more grooves  16, 18, 32, 34, 36, 40  in the wall of the flow line and radially outward of a generally cylindrical bore of the tubular. Each of the one or more grooves forms a spiral along the axial length of the flow line, thereby swirling fluid passing through the flow line and causing lighter fluid to move toward a center of the flow line due to a created vortex and heavier fluid to move toward a radially outer portion of the flow line.

FIELD OF THE INVENTION

This invention relates to devices and techniques for reducing or eliminating slugs in a tubular string within a well, such as liquid slugs in a gas well, or gas slugs in a liquid well or pipeline. More particularly, the device of the present invention is highly reliable and does not interfere with the passage of various tools through the tubular or pipeline.

BACKGROUND OF THE INVENTION

Various types of devices have been designed for reducing or eliminating slugs in a flow line. Slugs in a flow line may cause serious problems to downstream equipment, such as blow-out preventers, flow control valves, and sensors. Most slug prevention devices are positioned within the bore of the tubular string, and thereby substantially interfere with the passage of wireline tools, coiled tubing tools, pigs, or other devices intended to pass through the tubular string or pipeline.

U.S. Pat. No. 5,698,014 discloses a spiral or auger type separator particularly intended for well production fluid flow. U.S. Pat. No. 5,431,228 discloses another version of a liquid-gas separator for use in downhole producing wells. An early version of an air-water separator is disclosed in U.S. Pat. No. 4,762,176. U.S. Pat. No. 5,570,744 discloses another version of a separator for well production fluids, including a spiral baffle.

The disadvantages of the prior art are overcome by the present invention, and an improved slug reducer for use along a flow line is hereinafter disclosed.

SUMMARY OF THE INVENTION

According to a preferred embodiment, a flow line for reducing axial separation of different density fluids passing through the flow line includes one or more grooves in a wall of the flow line and radially outward of a generally cylindrical bore of the flow line. Each of the one or more grooves forms a spiral along an axial length of the flow line, thereby swirling fluid passing through the flow line and causing lighter fluid to move toward a center of the flow line due to a created vortex and heavier fluid to move toward a radially outer portion of the flow line.

In another embodiment, a tubular for reducing axial separation of liquid slugs and gas slugs passing through the tubular in a well includes one or more grooves in the tubular, with the one or more grooves each forming a spiral along the axial length of the tubular. Swirling fluid passing through the tubular in the well causes gas to move toward a center of the tubular due to the created vortex and liquid to move toward a radially outer portion of the tubular.

According to the method of the invention, axial separation of different density fluids passing through a flow line having a generally cylindrical bore is reduced by forming one or more grooves in a wall of a flow line and radially outward of the generally cylindrical bore of the flow line. The recesses may be formed by one or more radially outward projections on a mandrel, such that when the flow line moves axially over the mandrel while rotating, the one or more grooves are formed in the flow line.

These and other features and advantages of the invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a portion of a tubular and a portion of a coupling threadedly connected to the tubular, with a single spiral groove provided in both the tubular and the coupling.

FIG. 2 is a cross-sectional end view of another embodiment of a tubular with three circumferentially spaced grooves in the tubular.

FIG. 3 is a detailed view of a portion of the groove shown in FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates a flow line, such as an oil field tubular 10, threadedly connected to a coupling 12 by threads 14. The flow line 10 is provided with a single spiraling groove 16, and the coupling 12 is provided with a similar spiraling groove 18. It should be noted that the grooves 16, 18 may be on different spiral pitches, and is not critical that the end of the groove in one tubular be aligned with the beginning of the groove in the next tubular. It is a particular feature of the invention to provide grooves along a coupling, and in some embodiments couplings of an axial length of several feet or more may be used, such that the couplings interconnect tubular lengths and swirl the fluids to provide the axial separation.

FIG. 2 is a cross-sectional view of a tubular 30, such as a production tubing or drill pipe, which has three circumferentially spaced grooves, 32, 34 and 36, with the grooves spaced equal above the circumference above the tubular. In many embodiments, two or more circumferential grooves will be provided along a length of the tubular to achieve the desired effect.

FIG. 3 is a more detailed view of one of the grooves in a suitable tubular. As shown in FIG. 3, the groove has a radial depth 40, which a preferred embodiment is from 2% to 25% of a wall thickness of the flow line, and in many embodiments will be from 7% to 12% of the wall thickness of the flow line. FIG. 3 also illustrates that the groove has there circumferential width 44 which is from 2% to 50% of the bore internal diameter 46 of the flow line, and in many applications is from 5% to 25% of the bore internal diameter. Each of the grooves is thus formed along a substantial portion of an axial length of one or more interconnected tubular members, and/or is formed along a substantial portion of an axial length of one or more couplings each interconnecting two tubular members.

FIG. 3 also illustrates that each of the grooves preferably has radially inner edge 48 and radially outer edge 50 which each have a radius of from 10% to 40% of a radial depth 40 of the groove. This feature reduces stress in the tubular due to the grooves, and decreases the likelihood of paraffins, waxes, and other materials will build up adjacent the edges of the groove.

The size of the grooves in the pitch of the spiraling grooves which are preferred will depend to some extent upon the velocity of the fluid moving through the flow line. Higher velocity fluids will require less groove depth. In a preferred embodiment, the tubular may be of the type having a verified thickness, such as the thickness 42 of the tubular wall normally greater than conventional thickness of the tubular. In other applications, an increased wall thickness tubular may be utilized to maintain the desired strength of the tubular while still providing the spiraling grooves along the tubular.

According to a method of the invention, the grooves in the tubular may be formed by a machining operation. In a preferred application, however, the grooves may be formed when initially extruding the tubular. For this application, a mandrel may be provided with radially outward projections forming the grooves in the inner wall of the tubular. The tubular thus passes over the mandrel and is rotated at the desired rate to achieve the spiral pitch intended.

A flow line with a generally cylindrical bore having a bore internal diameter includes one or more grooves in the wall of the flow line according to a preferred embodiment of the invention. The grooves are thus radially outward of the generally cylindrical bore, with each groove forming a spiral along the axial length of the flow line, thereby causing fluid to swirl as it passes through the flow line and causing lighter fluid to move toward a radial center of the flow line due to the created vortex and heavier fluid to move toward a radially outer portion of the flow line. The improved flow line thus reduces axial separation of different density fluids, which in one embodiment may be liquid slugs or gas slugs passing though the flow line, and in another embodiment may be different density liquids. The grooves cause spiraling of the fluids passing through the flow line, and reduce axial separation of one type fluid from another type fluid. A slug of one fluid upstream of the spiral grooves which occupies all or substantial portion of the cross-section of the bore may thus be stretched by the spiral grooves, so that this fluid reaches a downstream facility and constitutes only a portion of the bore of the same diameter flow line. This axial stretching or separation of the fluid thus reduces the damage to the downstream equipment normally caused by a slug of one type fluid. In a preferred embodiment, two or more grooves are circumferentially spaced at substantially uniform circumferential spacing about the flow line. This spiraling of fluid in the flow line also has the potential benefit of improved separation efficiency for downstream equipment, since separation of, for example, the liquid and the gas passing through the flow line prior to arrival at the downstream facility may assist significantly in downstream separation, since substantially only liquid will be in the radially outer portion of the flow line, and substantially only gas will be in the radially inner portion of the flow line.

Although specific embodiments of the invention have been described herein in some detail, this has been done solely for the purposes of explaining the various aspects of the invention, and is not intended to limit the scope of the invention as defined in the claims which follow. Those skilled in the art will understand that the embodiment shown and described is exemplary, and various other substitutions, alterations and modifications, including but not limited to those design alternatives specifically discussed herein, may be made in the practice of the invention without departing from its scope. 

1. A flow line for reducing axial separation of different density fluids passing through the flow line, comprising: the flow line having a generally cylindrical bore with a bore internal diameter and one or more grooves in a wall of the flow line and radially outward of the generally cylindrical bore, the one or more grooves each forming a spiral along an axial length of the flow line, thereby swirling fluid passing through the flow line and causing lighter fluid to move toward a center of the flow line due to a created vortex and heavier fluid to move toward a radially outer portion of the flow line.
 2. A flow line as defined in claim 1, wherein each of the one or more grooves has a radial groove depth of from 2% to 25% of a wall thickness of the flow line.
 3. A flow line as defined in claim 1, wherein each of the one or more grooves has a groove depth of from 7% to 12% of a wall thickness of the flow line.
 4. A flow line as defined in claim 1, wherein each of the one or more grooves has a circumferential groove width flow line from 2% to 50% of the bore internal diameter.
 5. A flow line as defined in claim 1, wherein each of the one or more grooves has a circumferential groove width from 5% to 25% of the bore internal diameter.
 6. A flow line as defined in claim 1, wherein each of the one or more grooves is formed along a substantial portion of an axial length of one or more interconnected tubular members.
 7. A flow line as defined in claim 1, wherein each of the one or more grooves is formed along a substituted portion of an axial length of one or more couplings each interconnecting two tubular members.
 8. A flow line as defined in claim 1, wherein each of the one or more grooves has radially inner and radially outer edges each with the radius of from 10% to 40% of a radial depth of the groove.
 9. A flow line as defined in claim 1, wherein the flow line includes two or more grooves circumferentially spaced at a substantially uniform circumferential spacing about the flow line.
 10. A tubular for reducing axial separation of liquid slugs and gas slugs passing through the tubular in a well, comprising: the tubular having a generally cylindrical bore with a bore internal diameter and one or more grooves in a wall of the tubular and radially outward of the generally cylindrical bore, the one or more grooves each forming a spiral along an axial length of the tubular, thereby swirling fluid passing through the tubular and causing gas to move toward a center of the tubular due to a created vortex and liquid to move toward a radially outer portion of the tubular.
 11. A tubular as defined in claim 10, wherein the tubular is one of a production tubular and a drill pipe.
 12. A tubular as defined in claim 10, wherein each of the one or more grooves has a radial groove depth of from 2% to 25% of a wall thickness of the flow line.
 13. A tubular as defined in claim 10, wherein each of the one or more grooves has a circumferential groove width flow line from 2% to 50% of the bore internal diameter.
 14. A tubular as defined in claim 10, wherein each of the one or more grooves is formed along a substantial portion of an axial length of one or more interconnected tubular members.
 15. A tubular as defined in claim 10, wherein each of the one or more grooves is formed along a substantial portion of an axial length of one or more couplings each interconnecting two tubular members.
 16. A tubular as defined in claim 10, wherein each of the one or more grooves has radially inner and radially outer edges each with the radius of from 10% to 40% of a radial depth of the groove.
 17. A method of reducing axial separation of different density fluids passing through a flow line having a generally cylindrical line with a bore internal diameter, comprising: forming one or more grooves in a wall of the flow line and radially outward of the generally cylindrical bore, the one or more grooves each forming a spiral along an axial length of the flow line, thereby swirling fluid passing through the flow line and causing lighter fluid to move toward a center of the flow line due to a created vortex and heavier fluid to move toward a radially outer portion of the flow line.
 18. A method as defined in claim 17, wherein each of the one or more grooves is formed by providing one or more radially outward projections on a mandrel, the flow line moving axially over the mandrel while rotating to form the one or more grooves.
 19. A method as defined in claim 17, wherein each of the one or more grooves has a radial groove depth of from 2% to 25% of a wall thickness of the flow line; and each of the one or more grooves has a circumferential groove width flow line, from 2% to 50% of the bore internal diameter.
 20. A method as defined in claim 17, wherein each of the one or more grooves has radially inner and radially outer edges each with the radius of from 10% to 40% of a radial depth of the groove. 